This invention relates generally to rotor assemblies and, more particularly, to damper systems for damping vibrations induced to the rotor assemblies.
A gas turbine engine typically includes at least one rotor including a plurality of rotor blades that extend radially outwardly from a common annular rim. Specifically, in blisk rotors, the rotor blades are formed integrally with the annular rim rather than attached to the rim with dovetail joints. An outer surface of the rim typically defines a radially inner flowpath surface for air flowing through the rotor assembly.
Centrifugal forces generated by the rotating blades are carried by portions of the rims below the rotor blades. The centrifugal forces generate circumferential rim stress concentration between the rim and the blades that may be induced through the blades. Additionally, within blisk rotors, because of an absence of friction damping created when dovetails and shrouds contact each other during operation, vibrational stresses may be induced to the rotor assembly.
To facilitate vibration damping, rotor assemblies may include dampers. At least some known rotor assemblies include sleeve dampers positioned beneath the rim to damp airfoil modes. The sleeve dampers provide damping to airfoil modes that have significant rim participation.
At least some other known rotor assemblies include rotor blades including pockets formed within the blades. A layer of damper material is embedded in the pocket and covered with a titanium constraining layer. The pocket is covered with a titanium cover that is welded to the rotor blade. During operation, forces induced within the rotor blade may cause the constraining layer to separate from the damper material and forcibly contact the cover. Over time, continued contact between the constraining layer and the cover sheet may cause the cover sheet to separate from the rotor blade.
In an exemplary embodiment, a multi-stage rotor assembly for a gas turbine engine includes a damper system for facilitating damping vibrations induced to the rotor assembly. More specifically, the rotor assembly includes a blisk rotor including a plurality of rotor blades and a radially outer rim. The rotor blades are integrally formed with the outer rim and extend radially outward from the rim. The damper system is attached to the rotor blades forming at least one stage of the rotor assembly, and includes at least one layer of damping material and a cover sheet. The cover sheet is attached to the rotor blade with adhesive to secure the damping material against the rotor blade.
During operation, as the rotor assembly rotates, the adhesive placed between the cover sheets and the rotor blades carries centrifugal loads induced through the rotor blades. Vibration damping is facilitated by the damper system. More specifically, as the rotor assembly rotates, shear strains induced into the damper material facilitate vibration damping. As a result, the damper assembly facilitates damping vibrations induced to the rotor assembly in a reliable and cost-effective manner.